1. Field of the Invention
The present invention relates to a disparity value deriving device, an equipment control system, a movable apparatus, a robot, and a disparity value deriving method.
2. Description of the Related Art
In recent years, vehicle-mounted systems have generally been used for preventing automobile collisions by measuring the distance between automobiles or the distance between an automobile and an obstacle. Methods of measuring the distance include a method based on a stereo matching process using the principle of triangulation using a stereo camera having two cameras.
The stereo matching process is a process of obtaining disparity by matching corresponding regions with each other between a reference image captured by one of the cameras and a comparison image captured by the other camera, and calculating the distance between the stereo camera and an object included in the images from the disparity. The calculation of the distance to an object by this stereo matching process using a stereo camera enables a variety of recognition processing, and brake control and steering control for preventing collisions.
The stereo matching process as described above includes the block matching method in which, in order to evaluate the similarity between images, regions are cut out from the images to be compared and, for example, the sum of absolute differences (SAD) of luminance, the sum of squared differences (SSD), and the zero-mean normalized cross-correlation (ZNCC) are obtained for the regions. However, it is difficult to extract image features in a portion where texture in an image is weak, and the block matching method may not provide accurate disparity. A technique is then proposed as a method for deriving precise disparity, in which not only the cost of a pixel in a comparison image for a corresponding reference pixel in a reference image but also the costs of pixels in the neighborhood of the pixel in the comparison image are aggregated to derive a disparity value for an object with weak texture (see Japanese Patent Application Laid-open No. 2012-181142).
However, the technique disclosed in Japanese Patent Application Laid-open No. 2012-181142 derives disparity values for the entire image obtained by a stereo camera, disadvantageously requiring high memory consumption and involving a heavy image processing load.